The present invention relates to a lens frame holding device for an optical unit such as may be used in a copying machine.
In general, devices of this type includes, as shown in FIGS. 1 and 2, a cylindrical lens frame 12 holding a lens 11 and fixedly mounted on a housing 13. The housing 13 has two vertical walls 14 which are arranged perpendicular to the optical axis of the lens 11, and a bottom wall 15 connecting the vertical walls 14. Thus, the housing 13 is substantially U shaped in section. Cuts 16 for receiving and supporting the lens frame 12 are formed in the vertical walls 14 opening upwardly. A hook 17 and a threaded hole 18 provided on opposite sides of the middle portion of the bottom wall 15 hold a tying band 20. The tying band 20 has a hook receiving hole 21 at one end into which the hook 17 is inserted, and an attachment part 22 at the other end which has a through-hole. After the hole 21 is engaged with the hook 17, the attachment part 22 is fixedly secured to the housing 13 with a screw 23 to thus fixedly support the lens frame 12 on the housing. The housing 13 has a guide bar 19 for moving the housing 13 and accordingly the lens frame 12.
The above-described conventional lens frame holding device suffers from difficulties in that the middle portion of the lens frame 12, as viewed in the direction of the optical axis, is pushed downwardly by the typing band 20, while both end portions are pushed upwardly by the vertical walls 14. Therefore, if the force of tightening the typing band is excessive, the lens frame 12 will be bent, and accordingly the lens 11 inclined in the lens frame 12. In order to eliminate this difficulty, it is necessary to increase the accuracy of the components, with the result that the manufacturing cost becomes high. Furthermore, as the assembly process of the device includes a step of tightening the tying band with the screw 23, the assembling efficiency is relatively low. The position of the lens frame 12 on the housing 13 is regulated by the supporting cuts 16. However, no means for regulating the position of the lens frame in the direction of the optical axis is provided. Therefore, if the lens frame 12 is removed from the housing, for instance, for maintenance, then it is difficult to accurately reassemble the lens frame at the original position.